Renault insists it will not rush through planned upgrades to its engine for this season until it knows they will deliver a step forward in performance, even if that means they only appear at the tail-end of the season.

The French car manufacturer still has all 12 of the development tokens that it started the year with, having spent the first half of the campaign focused more on solving its reliability issues.

The upgrades had originally been pencilled in for this weekend's Russian Grand Prix, but with Renault still validating the changes that has slipped back.

There is a chance the tokens could be unleashed for the United States Grand Prix, but it is understood unless the tweaks deliver a good performance step and do not compromise reliability then it could be shuffled even further back.

When the upgrade is given the green light, Renault's Red Bull and Toro Rosso teams will have to decide how that fits in with their engine duty cycle.

Introducing the unit would deliver a grid penalty, so teams will have to balance out the potential gains of more power against the handicap of a lowly qualifying position for the first weekend.

Daniel Ricciardo said at the Japanese Grand Prix that he was not getting his hopes up too high about the upgrade though.

"We will take what we can get," he said. "But to be honest it is not going to be a 40bhp upgrade. I think it is better than what we have got now, but I wouldn't get too crazy about it.

"I will take it. It will not be half a second because from what I have heard it is not that much, it is on the cusp."